"Lending" page memory fatal error for member

To reproduce:
1. go into BBCLibraryPortage's account. (on production or dev site)
2. go to "Your books" page
3. open the "Lending" sub-page and let it load.

Bug: getting fatal error for memory when the page finishes loading: "Fatal error: Allowed memory size of 524288000 bytes exhausted (tried to allocate 2 bytes) in ?var/www/html/inc_circulation_stats/php on line 113"

NB: this is one of a handful of fatal errors we've been getting all over the site for members over the last week or so, for various reasons.

Okay, giving to Lucy. This may be hard. Ask for help if you need it. The key question is what the heck is taking up so much memory? We could increase it over 500MB, but this is not an okay problem to have with 10k books.

>2 timspalding: worth noting: I don't think it's the number of books but the "Lending" tab loading lending data. The library has over 400 patrons and over 42,000 lending transactions in their history.

Fixed by increasing memory allowance at this point.